1. Field of the Invention
The invention relates to a method for providing an improved four layered resistive ribbon transfer tape, characterized by the step of promoting good adhesion of a resistive layer to a metalized substrate.
2. Prior Art
Electrothermic printing devices are well known in the art. U.S. Pat. No. 3,744,611 to Lucio Montanari et al discloses one such device. An electrothermal printer for non-impact printing on plain paper makes use of a ribbon made up of a substrate having a thermal transferable ink coated on the surface towards the plain paper and a coating of an electrically resistant material on the other side. The ribbon is held in contact with the paper while a plurality of selectively energizable electrodes are held in contact with the resistive material coated side of the ribbon. The electrodes are selectively energized by causing a current to pass through an incremental portion of the resistive material to another electrode which is held in contact with said resistive material a short distance from said selectively energizable electrodes. The current in the incremental portion of the resistive material causes enough I.sup.2 R heating to soften the wax coated on the substrate directly opposite to the heated portion. The softened ink transfers to the plain paper sheet as a dot or a line.
The described device uses a three layered ribbon, with an insulating substrate having coated on one of its surfaces a resistive layer and on the opposing surface a thermal transferable ink layer. The disadvantage of this type ribbon is that diffused printing occurs due to lateral spread of the current from the electrode into the plane of the resistive layer.
To overcome the disadvantages of the above mentioned, a three layered resistive ribbon, a four layered ribbon has been devised. This four layered ribbon is comprised of a strength giving substrate layer having coated on one of its surfaces a conducting metal film which has disposed thereon a resistive film. On the opposing surface of said substrate layer is a thermally transferable ink film.
A serious problem incurred during the fabrication of the four layered resistive ribbons is the non-adherence or poor adherence of the resistive layer to the metal film. Separation of the layers often occurs as does corrosion of the conducting film. Thus, good adhesion of the resistive layer to the conducting film is extremely important.
It has been discovered here that the adherence problem is overcome by applying an adhesion promoter selected from among alkoxysilane compounds having the general formulae: ##STR1## Where R is an alkane group having from 1-5 C atoms. Y is from 1 to 18 carbon atoms and X is from 1 to 18 carbon atoms; and EQU (R--O).sub.3 --Si--(CH.sub.2).sub.n --NH.sub.2
Where R is an alkane group having from 1-5 C atoms and n is from 1-18.